This invention relates to a disk-array apparatus for use in combination with a host which serves as an upper-layer data processing apparatus such as a computer apparatus and which can write/read data to/from said disk-array apparatus and having a plurality of disk-medium modules and, in particular, to the disk-array apparatus further having a disk cache interposed between the host and the disk-medium modules for temporarily memorizing the data.
Generally, the disk-array apparatus has the disk cache (cache memory) in order to accelerate an access speed by the host to the disk-array apparatus. When the host performs a writing process (step) for writing data to the disk-array apparatus, writing data to be written into the disk-array apparatus are temporarily memorized in the disk cache. When the writing data is temporarily memorized in the disk cache, the disk cache or the disk-array apparatus performs a fast-write process. The fast-write process serves to inform to the host that the writing process is completed.
In the fast-write process, when the writing data transmitted from the host is memorized in the disk cache (a memory module), the above-mentioned information expressing that the writing process is completed is informed to the host. Therefore, the writing data to be updated may be disappeared or vanished by unexpected error before the writing data is practically written in the disk-array apparatus. This is called a data loss. In order to avoid the data lops, it is necessary to make the writing data into duplex data by providing backing-up data. Namely, the disk-array apparatus generally duplicates the writing data to make the duplex data by providing dual memory modules in order to avoid the data loss.
By making the writing data into duplex data as mentioned above, the disk-array apparatus will have redundancy.
However, if one of the memory modules of the disk-array apparatus fails, the memory modules perform degraded or degenerate mode by the other one of the memory modules. In case where the memory modules are operated in the degraded mode, the redundancy is spoiled. If the other one of the memory modules fails when the disk-array apparatus spoiling the redundancy performs the fast-write process, the writing data may be damaged.
On the other hand, if the fast-write process is forbidden, without exception, during the memory modules perform in the degraded mode, the writing data will not be damaged although the other one of the memory modules fails. However, the writing process will not be increased in transmission speed. Namely, the disk-array apparatus undesirably and considerably reduced in its performance.
The above-mentioned points are both very important for the disk-array apparatus to perform the writing process in high transmission speed and to avoid the data lose. Therefore, they are preferable and necessary for the disk-array apparatus to perform the writing process in high transmission speed and to avoid the data loss at the same time.
It is an object of this invention to deal with disadvantages mentioned above and to therefore provide a disk-array apparatus to be used for a host capable of performing a writing process in high transmission speed and to surely avoiding a data loss at the same time.
The other object, features, and advantages of this invention will become clear as the description proceeds.
This invention is directed to a disk-array apparatus for use in combination with a host which serves as a data processing apparatus, the disk array apparatus comprising a plurality of disk-medium modules, a plurality of memory modules, and a director module connected to the hose, the disk-medium modules, and the memory modules, the director module being for carrying out writing and reading operations of writing and reading the data to and from the disk-medium modules under control of the host and for temporarily storing the data to the memory modules when the director module carries out the writing and the reading operations. The memory modules comprise a first through a fourth memory modules. The first and the second memory modules are combined with each other so as to serve as a first memory module-pair. The third and the fourth memory modules are combined with each other so as to serve as a second memory module-pair. The director module writes, when a failure occurs in the fist memory module, fast-write data to the second and the fourth memory modules of the second memory module-pair and appoint two memory modules optionally selected from the second through the fourth memory modules for respectively performing cache control regions.